U.S. patent number 11,243,480 [Application Number 17/057,536] was granted by the patent office on 2022-02-08 for system for making accurate grating patterns using multiple writing columns each making multiple scans.
This patent grant is currently assigned to Applied Materials, Inc.. The grantee listed for this patent is Applied Materials, Inc.. Invention is credited to Hwan J. Jeong, David Markle.
United States Patent |
11,243,480 |
Markle , et al. |
February 8, 2022 |
System for making accurate grating patterns using multiple writing
columns each making multiple scans
Abstract
A lithography system for generating grating structures is
provided having a multiple column imaging system located on a
bridge capable of moving in a cross-scan direction, a mask having a
grating pattern with a fixed spatial frequency located in an object
plane of the imaging system, a multiple line alignment mark aligned
to the grating pattern and having a fixed spatial frequency, a
platen configured to hold and scan a substrate, a scanning system
configured to move the platen over a distance greater than a
desired length of the grating pattern on the substrate, a
longitudinal encoder scale attached to the platen and oriented in a
scan direction and at least two encoder scales attached to the
platen and arrayed in the cross-scan direction wherein the scales
contain periodically spaced alignment marks having a fixed spatial
frequency.
Inventors: |
Markle; David (Pleasanton,
CA), Jeong; Hwan J. (Los Altos, CA) |
Applicant: |
Name |
City |
State |
Country |
Type |
Applied Materials, Inc. |
Santa Clara |
CA |
US |
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Assignee: |
Applied Materials, Inc. (Santa
Clara, CA)
|
Family
ID: |
1000006099252 |
Appl.
No.: |
17/057,536 |
Filed: |
May 31, 2019 |
PCT
Filed: |
May 31, 2019 |
PCT No.: |
PCT/US2019/035049 |
371(c)(1),(2),(4) Date: |
November 20, 2020 |
PCT
Pub. No.: |
WO2020/009762 |
PCT
Pub. Date: |
January 09, 2020 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20210191285 A1 |
Jun 24, 2021 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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62693787 |
Jul 3, 2018 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G03F
7/70275 (20130101); G03F 7/70475 (20130101); G02B
5/1842 (20130101); G03F 9/7003 (20130101); G02B
5/1819 (20130101); G02F 2201/30 (20130101) |
Current International
Class: |
G03F
7/20 (20060101); G03F 9/00 (20060101); G02B
5/18 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Other References
International Search Report and Written Opinion dated Sep. 11, 2019
for Application No. PCT/US2019/035049. cited by applicant.
|
Primary Examiner: Asfaw; Mesfin T
Attorney, Agent or Firm: Patterson + Sheridan, LLP
Claims
What is claimed is:
1. A lithography system comprising: an imaging system located on a
bridge capable of moving in a cross-scan direction; a mask having a
grating pattern with a fixed spatial frequency located in an object
plane of the imaging system and a multiple line alignment mark
aligned to the grating pattern and having a fixed spatial
frequency; a platen disposed on a movable stage and configured to
hold a substrate; a scanning system configured to move the platen
in a scan direction over a distance greater than a desired length
of the grating pattern on the substrate, the scanning system
further configured to move the platen in the cross-scan direction;
a longitudinal encoder scale attached to the platen along a first
side of the platen and oriented in the scan direction; and at least
two encoder scales attached to the platen and arrayed in a
cross-scan direction, wherein the at least two encoder scales
contain periodically spaced alignment marks having a fixed spatial
frequency, the at least two encoder scales comprising a first
encoder scale along a second side of the platen and a second
encoder scale along a third side of the platen opposing the second
side, and the longitudinal encoder scale extending between the
first encoder scale along the second side and the second encoder
scale along the third side.
2. The system according to claim 1, wherein the imaging system is a
Dyson optical imaging system.
3. The system according to claim 2, wherein the Dyson optical
imaging system is a half Dyson optical imaging system.
4. The system according to claim 1, further comprising: a laser
illumination source.
5. The system according to claim 4, wherein the laser illumination
source is configured to have a TM.sub.00 lateral mode.
6. The system according to claim 1, wherein at least one of the at
least two encoder scales is arrayed in the cross-scan direction to
position in the cross-scan direction, every projected strip of the
grating pattern.
7. The system according to claim 1, further comprising: an
alignment system configured to view an image of an alignment mark
from a mask imaged on an encoder mark thereby generating a beam
that is modulated as the alignment mark is moved across the encoder
mark.
8. The system according to claim 7, wherein the alignment mark
comprises from 3 to 7 equi-spaced lines having a same period as the
grating pattern on the mask.
9. The system according to claim 1, wherein the longitudinal
encoder scale oriented in the scan direction and the at least two
encoder scales arrayed in the cross-scan direction facilitate a
platen path along a straight line, the longitudinal encoder scale
and the at least two encoder scales further configured to
facilitate a platen orientation constant with respect to an axis
normal to the platen.
10. The system according to claim 1, wherein the imaging system is
configured to produce two images simultaneously.
11. A method to perform lithography, comprising: placing a
substrate on a platen in a first position, the platen comprising: a
longitudinal encoder scale attached to the platen along a first
side of the platen and oriented in a scan direction; a first
encoder scale attached to the platen along a second side of the
platen and arrayed in a cross-scan direction; and a second encoder
scale attached to the platen along a third side of the platen
opposite the second side and arrayed in a cross-scan direction, the
first and second encoder scales each comprising periodically spaced
alignment marks having a fixed spatial frequency, and the
longitudinal encoder scale extending between the first encoder
scale along the second side and the second encoder scale along the
third side; imaging a grating pattern on the substrate with an
imaging system while moving the platen with a scanning system to
produce a first strip of imagery while using a metrology system to
ensure that the platen travels in a straight line without rotating
about an axis normal to the substrate surface; and indexing the
imaging system in the cross-scan direction to a second position
such that the second position is arranged wherein a second scanning
results in a second strip of grating imagery aligned with the first
strip of imagery.
12. The method according to claim 11, further comprising: using the
longitudinal encoder to ensure the scanning system moves without
rotating the platen about an axis normal to the substrate
surface.
13. The method according to claim 11, wherein the imaging is
performed with a Dyson imaging system.
14. The method according to claim 11, further comprising: using an
alignment system to check an alignment of the platen to the
encoder.
15. The method according to claim 11, wherein the imaging is
performed with a half Dyson optical imaging system.
16. The method according to claim 11, wherein a movement of the
substrate is approximately 2 m/s.
17. The method according to claim 11, further comprising: using an
alignment system to check an alignment of the platen to the
longitudinal encoder and the first and second encoder scales.
18. A method to align a substrate on a platen for performing
lithography, comprising: placing the substrate on the platen in a
first position, the platen comprising: a longitudinal encoder scale
attached to the platen along a first side of the platen and
oriented in a scan direction; a first encoder scale attached to the
platen along a second side of the platen and arrayed in a
cross-scan direction; and a second encoder scale attached to the
platen along a third side of the platen opposite the second side
and arrayed in a cross-scan direction, the first and second encoder
scales each comprising periodically spaced alignment marks having a
fixed spatial frequency, and the longitudinal encoder scale
extending between the first encoder scale along the second side and
the second encoder scale along the third side; imaging a mask with
an alignment target onto an alignment target on the platen;
generating an alignment signal based upon the imaged mask and the
alignment target; and tilting a primary mirror in a column based on
the alignment signal to center the image of the mask alignment
target on to the alignment target on the platen.
19. The method of claim 18, further comprising: scanning an image
of the mask alignment target across the alignment target on the
substrate, wherein the scanning is performed by the tilting primary
mirror; receiving image data from the scanning of the image of the
mask across the substrate; identifying a center peak position of
the received image data to the alignment target on the substrate to
calculate a deviation; and aligning the mask alignment target to
align with the substrate according to the deviation.
20. The method according to claim 18, wherein the imaging is
performed with a Dyson imaging system.
Description
BACKGROUND
Field
Aspects of the disclosure relate to flat panel display
manufacturing for various type of electronics. More specifically,
aspects relate to systems and methods for manufacturing wire grid
polarizers wherein the manufacturing systems that produce such
polarizers have grating patterns produced by multiple columns each
making multiple scans.
Description of the Related Art
There is a need in every liquid-crystal television set for a set of
efficient polarizers each of which is configured to transmit one
polarization of light and reflect an orthogonal polarization. These
polarizers are approximately the same size as a television picture,
thus with ever increasing sizes of televisions, polarizers of
greater than 66 inches in diagonal measure are needed. Wire grid
polarizers are generally constructed from an array of microscopic
wires on a glass substrate (or wafer) which selectively transmit
polarized light. Polarizers are a significant cost element for flat
panel monitors and such polarizers can account for as much as 30%
of the total cost of the flat panel system.
The increasing size of televisions and flat panel monitor systems
has stimulated an increase in the size of substrates from which
television screens are constructed, with some approaching three
meters square in size. In order to be commercially viable, it is
necessary to produce fine grating patterns on glass substrates over
a desired surface in as little time as possible including the
loading and unloading times so that the fine grating patterns meet
the specific polarization needs of the electrical device. The size
of the grating lines and spaces can be on the order of 50-100 nm,
and these grating lines are evenly spaced so as to not cause
noticeable defects in the resulting picture created for the
user.
In order to expose a grating over such as large area in a
relatively short period of time, it is necessary to employ multiple
optical columns, each of which write multiple strips of grating
pattern. A typical problem with this scheme is achieving and
maintaining proper alignment of the projected grating pattern with
respect to both the previous grating strip done by the same optical
column and with regards to the strips printed by adjacent columns.
As a non-limiting example, if the projected grating pattern has 100
nm lines and spaces and the lines in the projected grating are 0.2
mm long, then in order to prevent significant image smearing, the
direction of travel of the substrate needs to be aligned to the
direction of the grating lines so that the amount of smear is less
than 10 nm over a 0.2 mm length. The angular alignment between the
direction of the grating lines on the mask and the scan direction
of the stage should be within 10 nm/0.2 mm=1 part in 20,000 or
about 10.3 seconds of arc. Such angular alignment, in conventional
systems, is extremely difficult to achieve and maintain.
Another problem that conventional systems have is that substrate
must be stepped in the cross-scan direction with respect to the
columns between successive scans with a very accurate precision in
order to avoid image smearing where tapered images overlap. If such
cross-stepping is not accurately performed, the accumulated error
in the last scan will not be aligned correctly with the first scan
done by the adjacent column.
There is a need to provide a system and method to allow for making
accurate grating patterns using multiple writing columns and to
allow for the multiple grating strips generated in each scan to be
accurately aligned and uniformly exposed over the entire substrate
surface thus providing a polarizing grid having a very high
efficiency.
SUMMARY
The following summary should not be considered to limit the aspects
of the disclosure.
In one non-limiting embodiment, a lithography system is disclosed
comprising multiple imaging systems located on a bridge capable of
moving in a cross-scan direction, a mask having a grating pattern
with a fixed spatial frequency located in an object plane of each
imaging system and a multiple line alignment mark aligned to the
grating pattern and having a fixed spatial frequency, a platen
configured to hold and position a substrate, a scanning system
configured to move the platen over a distance greater than a
desired length of the grating pattern on the substrate, a
longitudinal encoder scale attached to the platen and oriented in a
scan direction and at least two encoder scales attached to the
platen and oriented in the cross-scan direction wherein the scales
contain periodically spaced alignment marks having a fixed spatial
frequency.
In one non-limiting embodiment, a method to perform lithography is
disclosed comprising placing a substrate on a platen in a first
position, imaging the grating pattern on the substrate while moving
the substrate with a scanning system to produce a first scan while
using an encoder scale and readouts to define the scan path and
angular orientation of the substrate, indexing the bridge holding
the optical columns to a second position with respect to the
scanning system such that the second position is arranged wherein a
second scanning a second exposure strip aligned adjacent with the
first exposure strip and thus extending the width of the exposure
area.
Other aspects and advantages will become apparent from the
following description and the attached claims.
BRIEF DESCRIPTION OF THE DRAWINGS
So that the manner in which the above recited features of the
present disclosure can be understood in detail, a more particular
description of the disclosure, briefly summarized above, may be had
by reference to embodiments, some of which are illustrated in the
appended drawings. It is to be noted, however, that the appended
drawings illustrate only typical embodiments of this disclosure and
are therefore not to be considered limiting of its scope, for the
disclosure may admit to other equally effective embodiments.
FIG. 1 is a plan view of a system for making accurate grating
patterns using multiple writing columns each making multiple
scans.
FIG. 2 is a plan view of a Dyson phase shifting, reflective reticle
used in a Dyson imaging system, which identifies the main features
on the reticle.
FIG. 3 is a cross-section of an alignment grating target contained
on a Dyson system mask. Ideally this target is also fabricated as a
reflective phase shift device.
FIG. 4 is a depiction of the two reflective areas on a Dyson
primary that collect the diffraction orders from the mask target
and image the orders onto a similar target contained on either end
of the platen.
FIG. 5 illustrates the amplitude of the diffraction orders created
by alignment target at the pupil of the primary mirror surface of
the Dyson system. Only two portions near the two peaks are
reflected to form the image of the alignment target on the
platen.
FIG. 6 is the image amplitude on the platen that results from the
truncated amplitude reflected from the primary mirror.
FIG. 7 is a graph of resultant target image intensity generated by
the amplitude shown in FIG. 6 wherein the loss of the zero order
has resulted in doubling the modulation frequency shown in FIG.
6.
FIG. 8 is a graph representing the target on the platen that is
repeated to form the encoder pattern on either end of the platen
wherein the reflective pattern can employ either phase of amplitude
modulation characteristics.
FIG. 9 is a graph of the zero order diffraction amplitude at the
pupil of the Dyson system. The zero order is generated by
reflection of the mask target image from the matching target on the
platen.
FIG. 10 is a graph of the amplitude at a detection plane, where the
mask and platen targets are imaged.
FIG. 11 is a graph of intensity at a detector plane, when the
targets are aligned.
FIG. 12 is a graph of signal intensity vs. the lateral shift
between the mask target and the target on the platen.
To facilitate understanding, identical reference numerals have been
used, where possible, to designate identical elements that are
common to the figures. It is contemplated that elements disclosed
in one embodiment may be beneficially utilized on other embodiments
without specific recitation.
DETAILED DESCRIPTION
In the following description, reference is made to embodiments of
the disclosure. It should be understood, however, that the
disclosure is not limited to specific described embodiments.
Instead, any combination of the following features and elements,
whether related to different embodiments or not, is contemplated to
implement and practice the disclosure. Furthermore, although
embodiments of the disclosure may achieve advantages over other
possible solutions and/or over the prior art, whether or not a
particular advantage is achieved by a given embodiment is not
limiting of the disclosure. Thus, the following aspects, features,
embodiments and advantages are merely illustrative and are not
considered elements or limitations of the appended claims except
where explicitly recited in a claim. Likewise, reference to "the
disclosure" shall not be construed as a generalization of an
inventive subject matter disclosed herein and shall not be
considered to be an element or limitation of the appended claims
except where explicitly recited in a claim.
Some embodiments will now be described with reference to the
figures. Like elements in the various figures will be referenced
with like numbers for consistency. In the following description,
numerous details are set forth to provide an understanding of
various embodiments and/or features. It will be understood,
however, by those skilled in the art that some embodiments may be
practiced without many of these details and that numerous
variations or modifications from the described embodiments are
possible. As used herein, the terms "above" and "below", "up" and
"down", "upper" and "lower", "upwardly" and "downwardly", and other
like terms indicating relative positions above or below a given
point or element are used in this description to more clearly
describe certain embodiments.
A system (arrangement) and method for making accurate grating
patterns for a wire grid polarizer for a flat panel display is
disclosed. The scanning stage may have an acceleration loading
limit placed upon the system for various reasons. For example, in
the embodiments described, a 0.5 g acceleration loading limit is
placed upon the system along with a maximum velocity limit of 2
m/s. Additional constraints may also be imposed. A set of
calculations may be performed by system architects to determine the
most cost-effective method of processing of the materials and the
resulting constraints may differ appreciably from the constraints
assumed in the following examples. It should be understood that
such calculations are merely illustrative and if greater speeds and
accelerations for preparing grating patterns are needed, the
calculations can be altered to provide for different results.
To calculate the time duration needed to perform a scan along a
typical arrangement (substrate) at a limit of 2 m/s as described
and imposed above: Acceleration/deceleration time (in
seconds)=Velocity/acceleration=(2 m/s)/(0.5.times.9.8
m/s.sup.2)=0.408 seconds
The time to scan the length of a 3 meter long panel (for a large
flat display) at a 2 m/s scan velocity is 1.5 seconds. The total
time to accelerate, scan the stage, and decelerate=0.408 sec+1.5
sec+0.408 sec=2.316 seconds.
It can therefore be observed that to cover an entire three (3)
meter wide panel with 20 mm wide strips of imagery to create a wire
grating pattern requires 150 scans. The total time, therefore, for
processing a single 3 by 3 meter square area would be 2.316 seconds
per scan.times.150 scans=347.5 seconds, when only one optical
column is used during the writing process. Such single column
processing is uneconomical to perform and a more economical
alternative is desired.
System designers have found that instead of providing a single
column process, a multiple column process where each column is used
to make multiple scans can be more economical as provided below.
Although described as making multiple scans, the systems and
methods may vary the number of scans to achieve a desired
efficiency.
To determine a number of scans, for example, that can be used to
process a three (3) meter wide thin-film panel, it is assumed that
the load and unload times for a stage 101 (with materials) is a
total 15 seconds. It is also desired to process an entire substrate
completely within one (1) minute in order to achieve compatibility
with the other operations in the factory Subtraction yields that
the amount of time to process the entire substrate (placing grating
patterns onto the substrate) is 1 minute total processing time-15
sec loading and unloading time=45 sec remaining for placement of
grating patterns.
The number of columns required to achieve a 45 second scanning time
is therefore 347.5 sec/45 sec=7.72 columns which rounds up to eight
(8) columns. With eight (8) columns being used in a simultaneous
process, only nineteen (19) strips are written by each column. In
the illustrated embodiment, therefore, eight (8) columns are used.
As one skilled in the art will recognize, a greater number of
columns may be used for processing and the processing will be
faster.
Referring to FIG. 1, a platen 100, which is movable, supports
(holds) a substrate 102. In the illustrated embodiment, the
substrate 102 may be a glass substrate with a surface coating that
is sensitive to exposure from a lithography process. Vacuum may be
used to clamp the substrate 102 to the platen 100. The platen 100
has two encoder scales 104, 106 that may be used to align the
bridge containing the optical columns and the position of the image
field in each column during processing. The two encoder scales 104,
106 consist of precisely placed alignment targets each consisting
of a group of 5 lines. In the illustrated embodiment, the bridge
100 is configured to move in 20 mm steps in a "y" direction of the
page. An array of lenses 108 positioned on the bridge is maintained
in alignment using the two encoder scales 104, 106 to check the
alignment after each stepping motion of the array of lenses 108.
The array of lenses 108 may be half Dyson optical imaging systems
that include a primary mirror, a positive lens and a reticle.
Alignment targets 110, 111 on the encoder strips 104, 106 are
arranged 20 mm apart such that movement of the lens array or the
position of an individual lens in the array of lenses 108 is
tracked with precision. The array of lenses 108 provide a means for
projecting images such as a grating pattern, as necessary, for the
embodiments described.
Moving the stage 101 in a straight line is achieved by placing the
two encoder scale readouts 118 and 119, mounted to ground and
aligned to the desired scanning direction along one side of the
platen 100 or chuck and deriving a signal therefrom that serves to
align the scan direction with the center of the encoder pattern
167. Scanning the stage 101 or stepping the bridge containing the
optical columns can be done by computer control such that
successive scans performed on the substrate 102 are aligned. The
scanning system 149 is configured to move back and forth precisely
on a straight line and after each scan the bridge is stepped in the
cross-scan direction to position the grating images for exposing
the next strip. Each step corresponds to a fixed, integral number
of grating periods. This can be done using an accurate encoder to
obtain a distance and then registering the projected grating
pattern alignment target against an alignment pattern built into
the platen 100 or chuck so the distance can then be used to
reposition the position of the column with respect to the substrate
at the ends of the scan travel.
In the illustrated embodiment, a grating image with 100 nm lines
and spaces is generated by imaging a grating pattern on a mask
having 200 nm lines and spaces with a 0.8875 NA, half Dyson optical
imaging system 116 using a laser 115 which as a wavelength of 355
nm. By eliminating any zero order diffraction from the image, the
spatial frequency of the image is doubled. Such a system 116 is
used to produce images for the lithography system 117. The laser
115 has a single lateral mode and may be used to create a
diffraction limited image. The exposure may also be tapered at the
ends of the grating pattern image and overlapped with a tapered
edge of a strip of imagery with another strip so that slight
registration errors between adjacent scans do not generate sharp
discontinuities discernable by the human eye. A grating image width
of 20 mm may be readily obtained from a modestly sized optical
column containing a 1:1 Dyson imaging system.
FIG. 1 illustrates the two encoder scales 104, 106 and their
positions on the platen 100 or chuck in order to keep the stepping
increment of the bridge constant and to ensure that a stepping
error does not appreciably blur the overlap area where the scans
overlap slightly. In this case, the platen 100 moves back and forth
along a single axis called the scan axis 112, which defines a scan
direction 113, which is horizontal in FIG. 1, and the bridge
containing the optical columns is stepped in the vertical direction
to separate the grating strips exposed in successive scans. A
longitudinal encoder scale 167 containing the long lines extending
along the bottom of the platen 100 serves to define the scan path
and to prevent any platen 100 rotation during the scan. Two read
out arrangements, 118 and 119, are positioned along the encoder
scale 167 which provide the signals defining the scan path and
inhibit platen rotation. The platen 100 position in the vertical
direction in FIG. 1 is obtained by summing the 2-encoder readout
arrangements. Platen rotation is proportional to the difference in
the two readouts. By maintaining the sum and difference at constant
values, the scan direction and the platen rotation are held steady
during scanning. As will be understood by those skilled in the art,
it is desired to maintain platen rotation to a minimum. The bridge
containing the optical columns may then be stepped to a position
where a second scan may be performed. Performing a scan may be
controlled by a computer or other similar arrangement.
The two encoders 104, 106 located at either end of the platen 100
contain a series of 5-line grating patterns 107 that may be used as
alignment targets. When an alignment target incorporated into a
mask is imaged onto and scanned over one of the alignment targets
on the platen, an alignment signal is generated and processed to
yield an offset between the actual and ideal positions of the next
grating strip. This error can be corrected either my moving the
entire bridge, which changes the position of the images generated
by every column or by tilting the primary mirror in the column
generating the offset so the mask target image is perfectly
centered on the platen target in the cross-scan direction. Fine
adjustment can be made by slightly tilting a primary mirror in the
projection system to slightly shift the position of the projected
image. Coarse adjustments require repositioning the optical column.
The two vertical encoder scales 104, 106 at either end of the
platen 100 have to be adjusted so that an off-set error measured on
one end corresponds to an identical error on the other end.
The Dyson Alignment System
A mask 204 in the Dyson alignment system contains a 200 nm line and
space grating pattern roughly 20 mm in length and 0.2 mm at a
maximum width. In the embodiment illustrated, the lines in the
grating pattern are accurately aligned with the scan direction,
according to a two-step process, otherwise the grating image will
be smeared as the lines are scanned across the substrate.
Aligning the grating line direction with the scan direction
encompasses a first step whereby a substrate containing a 5-line
target extending from one side of the substrate to the other is
aligned to the scan direction using a theta adjustment provided in
the platen. This is done by measuring the cross-scan position of
the substrate target at a fixed point in the Dyson field and at
various scan positions. Any difference in the substrate target
position indicates a misalignment between the direction of the
substrate target and the scan direction, which can be corrected by
adjusting the orientation of the substrate. Once the substrate
target is properly aligned, it is used to align the orientation of
the object grating pattern. In this case the substrate is held
still and the point in the Dyson field used to measure the offset
is varied and the Dyson mask is rotated until a null position is
achieved.
FIG. 2 is a schematic of the Dyson reticle 201 used in the Dyson
imaging system 205 used to making accurate grating patterns. In
this example, an aluminized phase grating pattern 202 consists of
200 nm lines and spaces and the narrow line extending vertically
down the center of the mask 204 is the mask alignment target, which
contains five lines 203 each 200 nm wide and spaced 400 nm apart.
The grating pattern 202 has a fixed spatial frequency. The
five-line alignment target 203 on the Dyson mask 204 can be
illuminated with a narrow beam of illumination having the same
wavelength as is used to form the grating image. The beam of
illumination can be switched from a position 6 mm above the grating
to a position 6 mm below. The two horizontal lines in FIG. 2
indicate the two possible positions for the focused laser beam on
the mask pattern. The mask pattern is illuminated with a Gaussian
beam that would result in a very non-uniform exposure if the
grating lines were all the same length. Consequently the grating
lines are made shorter in the center than at the ends in order to
achieve a constant exposure dose across the width of the field. The
image of the grating is projected through a window on the mask 207,
located on the opposite side of the system axis, which is centered
in the small circle of FIG. 2. The substrate focal plane is
immediately below the mask object plane, the illuminated positions
of the mask alignment target are also projected through the mask on
the opposite side of the optical axis. Thus target 203 is imaged at
203' and target 206 is imaged at 206'.
FIG. 3 depicts a cross-section of the alignment target contained on
the Dyson mask, and FIG. 4 depicts the two small reflective areas
on the Dyson primary that collect the .+-.1 diffraction orders from
the mask target and image them onto the substrate. The zero
diffraction order is lost. As can be seen in FIG. 3, the five lines
of the target are presented along a displacement axis (x) in um.
The center line of the five line group is centered along the x(um)
value of 0.
FIG. 5 illustrates the amplitude of the .+-.1 diffraction orders at
the pupil of the primary mirror surface. Since the reflective area
on the Dyson primary mirror is confined to 2 small reflective
areas, as illustrated in FIG. 4 (ending at -1.0 NA and 1.0 NA), the
diffraction amplitude spectrum is truncated between the bold
vertical lines 402, 404, 406, 408 on FIG. 5. The resulting
amplitude image taking into account the truncated diffraction
amplitude spectrum is shown in FIG. 6. This pattern is essentially
a fringe pattern in which the amplitude envelope is determined by
the numerical aperture of the reflector at the primary mirror.
FIG. 7 illustrates the resultant intensity of the mask target
image, having double the frequency of the amplitude spectrum shown
in FIG. 6, which results from squaring the amplitude spectrum. FIG.
8 represents the amplitude or reflected intensity from the platen
target on which the mask target image is superimposed. The detector
signal depends on a sum of the sampled amplitudes squared and this
sum can clearly be positive, negative or zero depending on the
relative positions of the projected mask alignment target and the
alignment target on the platen 100. Squaring these values inverts
the negative signals and doubles the frequency, but the zero values
remain.
FIG. 9 shows the amplitude of a diffraction-limited signal from a
1.8 micron wide line at the collection optics located on the axis
of the projection system and slightly behind the Dyson primary
vertex. The bold vertical lines 902, 904 in FIG. 9 indicate that
there is appreciable truncation at the collection aperture, which
results in the amplitude distribution shown in FIG. 10 and the
intensity distribution shown in FIG. 11. Scanning the image of the
five line mask 204 target across the matching 5-line target on the
substrate generates the signal shown in FIG. 12. Scanning is done
by tilting the primary mirror of the Dyson system about the mirror
vertex in the cross-scan direction with a precision motorized
micrometer. The center peak of this signal is easily identified,
and is about 200 nm wide. As a result, the mask target position is
clearly defined with respect to the platen target and can be
measured to within .+-.5 nm.
A challenge of writing with multiple columns concurrently is that
after writing 18 strips, the 19.sup.th strip must overlay the first
strip written by the adjacent column within .+-.10 nm. This
requires that the center of the image produced by each column is
precisely spaced with respect to the image centers of the adjacent
columns. This is achieved by incorporating a 5 line grating target
into the mask pattern used to form the grating image and by placing
similar 5 line grating target at selected points along the two
encoder scales shown in FIG. 1. The vertical calibration scale
serves to position the projected pattern positions of each column
and the position of each strip written by each column.
In one non-limiting embodiment, a lithography system is disclosed
having an imaging system optical column located on a bridge capable
of moving in a cross-scan direction, a mask having a grating
pattern with a fixed spatial frequency located in an object plane
of the imaging system, a multiple line alignment mark aligned to
the grating pattern and having a fixed spatial frequency, a platen
configured to hold and scan a substrate, a scanning system
configured to move the platen over a distance greater than a
desired length of the grating pattern on the substrate, a
longitudinal encoder scale attached to the platen and oriented in a
scan direction and at least two encoder scales attached to the
platen and arrayed in the cross-scan direction wherein the scales
contain periodically spaced alignment marks having a fixed spatial
frequency.
In another non-limiting embodiment, the arrangement is provided
wherein the imaging system is a Dyson optical imaging system.
In another non-limiting embodiment, the arrangement may be provided
wherein the Dyson optical imaging system is a half Dyson optical
imaging system.
In another non-limiting embodiment, the arrangement may further
comprise a laser illumination source. More specifically, the laser
illumination source is configured to generate a single T,0,0
lateral mode.
In another non-limiting embodiment, the arrangement may be provided
wherein at least one of the two encoder scales is arrayed in the
cross-scan direction to position in the cross-scan direction, every
projected strip of grating pattern.
In another non-limiting embodiment, the arrangement may further
comprise an alignment system configured to view an image of a mask
alignment target superimposed on a similar target contained in the
array of targets on the encoder strip attached to the platen
thereby generating a beam that is modulated as the mask alignment
mark image is moved across the encoder mark.
In another non-limiting embodiment, the arrangement may be
configured wherein the mask and platen alignment marks comprises
from 3 to 7 equi-spaced lines having the same period as the grating
pattern on the mask.
In another non-limiting embodiment, the arrangement may further
comprise a metrology system connected to the platen and configured
to enable the platen to repeatedly move along a the same straight
path while maintaining a fixed angular orientation with respect to
an axis normal to the substrate surface.
In another non-limiting embodiment, the arrangement may further
comprise at least two half-field Dyson optical columns configured
to write simultaneously and arranged such that grating pattern
strips written by each of the optical columns are equally spaced in
the cross-scan direction and form a continuous grating pattern once
all the stripes are written.
While embodiments have been described herein, those skilled in the
art, having benefit of this disclosure will appreciate that other
embodiments are envisioned that do not depart from the inventive
scope of the present application. Accordingly, the scope of the
present claims or any subsequent related claims shall not be unduly
limited by the description of the embodiments described herein.
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